CVE-2026-63829net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink

Official description

In the Linux kernel, the following vulnerability has been resolved: net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink A tunnel changelink() operates on at most two netns, dev_net(dev) and the tunnel link netns t->net. They differ once the device is created in or moved to a netns other than the one the request runs in. The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a caller privileged there but not in t->net can rewrite a tunnel that lives in t->net. Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is skipped when the link netns is dev_net(dev), where the rtnl path already checked it. The other patches in this series use the same helper. Gate ipgre_changelink() and erspan_changelink() with it, at the top of the op before any attribute is parsed, because the parsers update live tunnel fields first. ipgre_netlink_parms() sets t->collect_md before ip_tunnel_changelink() runs. Commit 8b484efd5cb4 ("ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().") added the same check on the ioctl path. This adds it on RTM_NEWLINK.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/19275943d8fe903eb7b9aa53e380e41efd042ada
• https://git.kernel.org/stable/c/866b0f5ae599490bd496fd84581c68ac8b94e6af
• https://git.kernel.org/stable/c/92b766fc55156e0da2ecd0c2302c971118f8a229
• https://git.kernel.org/stable/c/e54c05ed3d9c28733fb9e5837219aca3691defa3
• https://git.kernel.org/stable/c/9831bc9ecb402957810c2045c663fbfe9b09e296
• https://git.kernel.org/stable/c/1697957eb0971d420dde42862b88eb43506a1105
• https://git.kernel.org/stable/c/47b5d3d506609b08b2e1f7c14f0b681a1953d572
• https://git.kernel.org/stable/c/8165f7ff57d9667d2bb477ef6af83ede7fed4ad7